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October 8, 2011

Illinois Researchers Localize 3D Matter Waves

by editor

A new University of Illinois study, demonstrating how material defects can affect three-dimensional conduction, could profoundly alter ultrasonic waves used in medical imaging, lasers, superconductors, and more, the college reported in a press release Friday.

The study, which was led by physics professor Brian DeMarco, resulted in complete localization of quantum matter waves in three dimensions, which was reportedly originally theorized some 50 years ago. DeMarco and his colleagues published their findings in the latest edition of the journal Science.

"The impact of disorder on waves depends strongly on their energy in three dimensions," the University press release said. "The high-energy red wave can freely propagate outward through the disordered green laser in the experiment, but the low-energy blue wave is trapped, or localized, by reflections from the disorder."

While defects in materials are common, according to the researchers, their effects are often not understood. By trying to figure out how flaws in a material impacts how waves traveling through it, referred to as the "physics behind disorder" by DeMarco, could well be "fundamental to understanding the impact of unavoidable material imperfections on these kinds of applications," he said.

According to the press release, this is the first time that scientists have been able to observe "a phenomenon known as Anderson localization," which is defined as a "strong disorder" capable of creating "interference on all sides can trap a matter wave in one place."

DeMarco compared it to a trumpet player performing in a concert hall that had been filled with special barriers that reflect sound waves. Normally, the sound would travel in all directions, but due to the barriers' reflective properties, the sound remains at its source and there is complete silence throughout the entire concert hall.

"That´s exactly the case in our experiment, although we use quantum matter waves instead of sound, and the barriers are created using a speckled green laser beam," he said.

In order to simulate electrons moving in waves through a metal, DeMarco and his associates used ultra-cold atoms travelling together as laser light. According to the media release, the team demonstrated that the laser beam "could completely localize the atoms -- the first direct observation of three-dimensional Anderson localization of matter."

"This means that we can study Anderson localization in a way that is relevant to materials," DeMarco added. "Now, theories of Anderson localization in 3-D can be compared to our 'material' and tested for the first time."

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Image 1: An illustration of Anderson localization. The green balloons represent disordered barriers that localize the sound of the trumpet at its source. Photo by L. Brian Stauffer

Image 2: Physics professor Brian DeMarco, center, and graduate students Stanimir Kondov, left, and William McGehee were the first to trap waves of quantum matter in three dimensions. Photo by L. Brian Stauffer